Tube Amp Archive

The permeability usually suffers greatly from compression and from cold-hardening that occurs during stamping and most likely during bending. Most manufacturers employ annealing after stamping which cursory increases the permeability for 20-30% (250-300% for some alloys). However such an annealing p...

No, you need highly permeable magnetic material such as transformer steel.

A schematic would be very helpful to reduce confusion.

Well, there is the Vhk rating (heater to cathode voltage) for each tube that should not be exceeded. Also by saturating the leakage current you theoretically introduce a bit of regular noise, but I don't think this is of concern, especially in guitar amps.

I've only added the NFB defeat in my 6L6 champ. So it is like switching between presence and resonance bot at 0 and both at 10. Always loved the tone more without the NFB, but the difference is really subtle on a champ. Probably that's why.

If the buzz is 50/60Hz and not 100/120Hz, the aluminium foil won't work because it would more likely be magnetic interference.

What is the optimal p2p impedance in triode mode? Also, it seems that your master volume won't work all that well with the PP/SE knob. 85% plate dissipation is awfully bold for a PP while still cold for an SE, you won't like the sound once you turn off one of the valves I bet.

Well, if it is the fuse, it should be the power stage. Ideally, you need a tech to monitor both plat/cathode current on both tubes and their bias while you're playing. probably someone with a scope or at least a couple of voltmeters. If I saw the correct schematic, the bias circuit is not adjustable...

Basic rule of switching: don't switch DC. That includes plate supplies, cathodes (incl. NFB) etc. I assume that the cold clipper is the stage with a large cathode resistance. If you want to make it switchable/variable, you'll have to live with the noise - either popping of the relay/switch or the cr...

Cheers, guys! Finally I'm able to converse with someone who had read Merlin's books! Glad my Dumble research led me here

Nice screen compression pot! Might wanna wire one in on the test amp as well! Thanks for sharing. I myself am working on a last stage pentode design, however I've found the ECF80 tube to be really neat in terms of a pentode+CF in one envelope. We also have a nice abundant replacement model here in R...

Hi!

This is gain pot tone compensation, however in the second case it is a bit more funny. Here is the basic frequency response of these networks (The curves are 2-4-6-8-10 rotation of the pot):